When a load on an Alternating Current (AC) power source is not a linear load (i.e., the load is a non-linear load) the current being drawn from the AC power source may be out of phase with the voltage of the AC power source. A purely resistive load is a linear load. A load having an energy storage component (such as an inductance or a capacitance) may be a non-linear load. A load that draws power irregularly over the course of a cycle of the AC power source, such as a rectifier or a Switch Mode Power Supply (SMPS), may be a non-linear load.
When the current being drawn by a non-linear load from the AC power source is out of phase with the voltage of the AC power source, the current being drawn from the AC power source will be higher, on average, than it would be if the current and voltage were in phase. This can cause power to be wasted and damage to occur in the AC power source.
The degree to which the current drawn by a load from the AC power source is in phase with the voltage of the AC power source may be expressed as the Power Factor (PF) of the load. An ideal linear load has a PF of 1, and non-linear loads have a PF less than one.
A PFC circuit may be provided between an AC power source and a load. The PFC circuit operates to present a PF close to 1 (e.g., 0.98) to the AC power source by keeping the phase of current drawn from the AC power source close to the phase of the voltage of the AC power supply, even when the phase of the current drawn by the load is out of phase or irregular.
It is desirable for a PFC circuit to minimize line current distortion, that is, deviation of the line current away from proportionality with the line voltage. It is desirable for a PFC circuit to be as simple as possible and still meet its design objectives.
Those skilled in the field of the present disclosure will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments. This avoids obscuring the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures herein. The details of well-known elements, structures, or processes that are necessary to practice the embodiments and that are well known to those of skill in the art may not be shown and should be assumed present unless otherwise indicated.